"I feel like I have contributed all I can to this primary election, and it's clearly not my time," he said in an interview with MSNBC.

"So I am going to end my presidential campaign, continue my work as mayor of New York City and I'm going to keep speaking up for working people."

Mr de Blasio, 58, had launched his candidacy in May.

Observers say his campaign had failed to take off within a wide field of Democrats seeking to be selected as the party's presidential candidate.

President Donald Trump tweeted on Mr de Blasio's announcement, saying ironically that it was "really big political news".

Mr de Blasio told MSNBC that a "central reason" for his decision was the Democratic Party's rules for qualifying for televised debates.

"The bar is so high so early that for a lot of us - clearly, some of my fellow chief executives, governors - couldn't make that cut," he said.

He failed to qualify for a debate earlier this month that featured the 10 leading candidates for the party's nomination.

There are now 19 Democrats left in the running, with former Vice-President Joe Biden currently ahead in the polls, followed by left-wing senators Elizabeth Warren and Bernie Sanders.

The rest of the Democratic contenders have polled in single figures in most opinion polls.